BIOSYNTHESIS 261 



In the biosynthesis of glutamine from glutamate and ammonia it is the 

 y-carboxyl of glutamic acid which is activated, and the cleavage of ATP to 

 provide the 2500^000 calories for formation of the amide bond takes 

 place so that ADP and P are formed rather than AMP and PP. Glutamic 

 acid can also form amide bonds with hydroxylamine, hydrazine or 

 methvlamine. 



The enzyme system responsible for the synthesis catalyses the following 

 series of reactions (E = enzyme) : 



ATP 



(1) E + ATP + Glu^E 



\ 

 Glu 



ATP 



/ Mg-H- 



(2) E -f NH3 ^ Glu— NH2 + ADP + P -f E 



\ Mn+ + 



Glu 



According to Bloch and co-workers, the enzymatic synthesis of glu- 

 tathione, requires only ATP 



E + ATP - E— P + ADP 



E— P + Glu ^ E— Glu + P 



E — Glu -f Cys ^ E + Glu — Cys 



E— P + Glu— Cys ^ E— Glu— Cys + P 



E— Glu— Cys + Gly ^ Glu— Cys— Gly + E 



In these four cases of formation of amide or peptide bonds, it is the 

 carboxyl group which is activated at the expense of one or the other of the 

 pyrophosphate linkages of ATP. The syntheses differ from each other in 

 the form of the activated carboxyl : bound to CoA, bound directly to the 

 enzyme or to the phosphorylated enzyme. But in no case has the activated 

 carboxyl itself been phosphorylated. 



C. Biosynthesis of Macromolecules 



{a) Polysaccharides 



1. Synthesis of Glycogen 



As already stated, glycogen is a branched polymer made up of D-glucose 

 units. Four enzymes are necessary for the degradation of glycogen to 

 glucose, and for the synthesis of glycogen from glucose. Two of these 



